Regional Anesthesia for the Dentistry and Oral Surgery Patient

Dr. Mulherin is a Clinical Associate Professor at Iowa State University (ISU) College of Veterinary Medicine. She received her DVM from Iowa State University. Dr. Mulherin was a private practitioner before returning to ISU in the Primary Care Service. She completed her Dentistry and Oral Surgery residency at the University of Wisconsin-Madison, School of Veterinary Medicine, while maintaining her appointment at ISU. She became a Diplomate of the American Veterinary Dental College in 2015. She is currently the section leader of the Dentistry Service at ISU. Her focus is on education of veterinary students, recent graduates, and referring veterinarians.

Julie M. Riha
DVM Iowa State University, Ames, Iowa

Dr. Riha is a Clinical Assistant Professor at Iowa State University (ISU). Her main clinical focus is Emergency and Critical Care. She is a 2014 graduate of Ross University. She completed an internship at ISU and practiced for 2 years in an emergency private practice before accepting a faculty position at ISU. Her professional interests are toxicology and trauma patients.

Regional anesthesia, especially when combined with an opioid, can provide a more comfortable procedure for our canine and feline patients. Photo Credit: Shutterstock

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THE ANESTHETIC PROTOCOL

For canine and feline patients, multimodal pain management techniques should be used to try to lessen the amount of general anesthesia that is needed for a given dental procedure.

For most canine and feline patients, dental cleanings and thorough evaluation of the oral cavity is recommended at least annually.1 For these patients, general anesthesia is required for an accurate assessment of the health of the oral cavity and for a thorough performance of dental cleaning.1,2 According to the 2013 American Animal Hospital Association Dental Care Guidelines for Dogs and Cats, general anesthesia with a secured airway is necessary for proper assessment and treatment of canine and feline patients.1

However, general anesthesia in veterinary patients is not to be taken lightly. Clients have significant concerns and anxiety when thinking about their pets being placed under general anesthesia.

As practitioners, to help reduce the incidence of anesthetic-related complications, we should perform an accurate presurgical/preanesthetic assessment of each patient. A thorough physical examination, baseline screenings, and appropriate diagnostic testing to identify any underlying conditions will help us optimize the condition of the patient before the procedure.

In addition, we should consider adding regional anesthesia to the anesthetic protocol. Regional anesthesia decreases the patient’s dependence on general anesthesia, which benefits both the patient and the practitioner. This article emphasizes the benefits and describes the drugs and techniques involved in proper administration of regional anesthesia.

When a regional anesthetic drug is injected into canine and feline patients, it is imperative that the administrator first aspirate the syringe to avoid inadvertent intravenous injection.

ASSESSING PAIN

As veterinarians, we do not have the luxury of asking our patients if they are experiencing pain. However, the International Association for the Study of Pain states that the inability to communicate pain does not necessarily negate the possibility that pain is being experienced.3 Dogs and cats with dental disease experience discomfort that the client and general practitioner may not appreciate. According to the 2015 American Animal Hospital Association/American Association of Feline Practitioner Pain Management Guidelines for Dogs and Cats, an animal’s inability to self-report pain and discomfort leaves the assessment and recognition of pain with the veterinary professional.4 According to a 2014 survey of veterinary surgeons in the United Kingdom, among the top 3 perceived common causes of chronic pain in their patients was dental disease.5 This pain may not be appreciated by the practitioner or client until after the disease has been treated and the patient has resumed its prepain normal behavioral activities.4

WHAT IS PAIN?

As described by the International Association for the Study of Pain, pain is a sensory or emotional stimulus associated with actual or apparent tissue trauma that is perceived as unpleasant.6 The purpose of pain is to elicit a reaction from the body to prevent additional damage to the affected area. Response to a painful stimulus can range from hyperalgesia, an exaggerated response to a stimulus normally perceived as painful,7 to allodynia, a painful response to a stimulus that is not normally perceived as painful.7 When pain is incurred for an extended duration, central sensitization (windup) can occur. This response occurs when the associated neurons repeatedly fire at a lower than normal threshold8 and is commonly seen in patients suffering from chronic oral pain (e.g., severe periodontal disease).9

When tissue is injured, the painful response is recognized by the central nervous system through a process called nociception. Recognition and processing of the painful stimulus occur in 4 steps: transduction, transmission, modulation and perception.10

Transduction is the transformation of energy from a painful stimulus into nerve impulses by pain receptors.10 Transduction can be inhibited by multimodal pain-relieving methods (e.g., use of local anesthetics, nonsteroidal anti-inflammatory drugs, and opioids).11

Transmission is the movement of nerve impulses to the spinal cord and then to the brain.10 This process can be inhibited by use of local anesthetics, opioids, and alpha-2 agonists.

Modulation is the transmission of the painful stimulus at the spinal cord to be transmitted to the brain as pain or to inhibit further transmission to the brain.10

Perception is the method by which impulses are recognized as pain.10 Perception can be inhibited by administering opioids, alpha-2 agonists, anesthetics, and inhalants.11

Ideally, multimodal pain management techniques should be used to try to lessen the amount of general anesthesia that is needed for a given procedure. For dentistry and oral surgery, one of the most effective ways to help block a painful stimulus is to use regional anesthesia.

REGIONAL ANESTHESIA

For the dentistry and oral surgery patient, regional anesthesia can eliminate transduction and transmission, thereby decreasing pain perception and central sensitization.11 A study conducted in 2013 found that use of regional anesthesia reduced the minimum alveolar concentration of isoflurane needed without causing any adverse effects on the hemodynamic state of the patients.12 Keeping patients in a lighter plane of anesthesia increases client satisfaction because the patients recover quickly from the effects of anesthesia and are therefore less likely to be discharged with a drug “hangover.” Regional anesthesia helps create a painless transition from general anesthesia to consciousness and continues to work after the procedure to reduce patient discomfort and allow oral pain medication to begin working.

COMMONLY USED MEDICATIONS

Lidocaine

A short-acting medication that is commonly used for regional anesthesia is lidocaine. This medication is usually supplied as a 2% solution (20 mg/mL). It has a rapid onset of action (within 5 minutes)13 and a relatively short duration of action (60 to 120 minutes).14 If you want intraoperative pain relief only and would like to have the local anesthetic metabolized by the time the patient is awake, this drug would be the most appropriate choice for regional anesthesia. Cats are significantly more sensitive than dogs to this medication. Reported doses are 6 mg/kg for dogs and 3 mg/kg for cats.15 However, we prefer to use a maximum dose of 2 mg/kg in the dog and 1 mg/kg in the cat (TABLE 1). Note that the total dosage of this medication is additive. If lidocaine is being used as part of an induction agent or maintenance pain medication (e.g., constant rate infusion), the total dosage must not exceed 5 mg/kg in dogs.16 Our preference is to keep the dosage below 2 mg/kg in both canine and feline patients. A potential side effect of lidocaine administration is central nervous system excitation, which could result in convulsions.17

Bupivacaine

A longer-acting medication used for regional anesthesia is bupivacaine. This medication comes in different concentrations: 0.25% (2.5 mg/mL), 0.5% (5 mg/mL), and 0.75% (7.5 mg/mL). The onset of effect has been reported to be as short as 8 minutes and as long as 30 minutes, and the effect has been reported to last from 4 to 10 hours, depending on where it is placed. For cats, the toxic dose of this medication is greater than 2 mg/kg total dose.15 As with lidocaine, cats are also extremely sensitive to bupivacaine. The maximum dosage of this medication should never be exceeded. For dogs and cats, the recommended total dosage of bupivacaine is less than 2 mg/kg (Table 1).15 Unlike lidocaine, bupivacaine is not used in constant rate infusions because it is highly cardiotoxic. However, in dogs and cats, the total dosage for local blocks is additive. Complications include neurotoxic and cardiotoxic complications (e.g., tremors, seizures, coma, respiratory depression, profound cardiac depression, ventricular fibrillation, and asystole).18

When a regional anesthetic drug is injected into canine and feline patients, it is imperative that the administrator first aspirate the syringe to avoid inadvertent intravenous injection. We have never experienced any adverse side effects or complications when careful technique is used and recommended dosages are followed.

ADDITION OF AN OPIOID

An adjunctive medication that can be added to bupivacaine to extend the action of the regional block is buprenorphine. We recommend that buprenorphine be added to the regional block at a dose of 15 mcg per patient. Studies have shown that when bupivacaine was combined with an opioid such as buprenorphine, it increased the duration of action of the local anesthetic agent by threefold.19,20 In a study evaluating the effect of adding buprenorphine to bupivacaine in an infraorbital nerve block and its effects on the minimum alveolar concentration of isoflurane, the anesthetic requirement for patients that received the combination was less than that for patients that received bupivacaine alone.21 The same study also provided support for prolonged regional anesthetic effects.21 The authors speculated that the addition of buprenorphine to a regional anesthetic block may extend the duration of the block to 48 to 96 hours after administration instead of 4 to 10 hours without buprenorphine.21

REGIONAL ANESTHESIA TECHNIQUE

Regional anesthesia is safe for the patient as long as the administrator has a grasp of the anatomy surrounding the region to be injected and uses safe technique. Because regional anesthesia is administered when the patient is under general anesthesia, it can be invasive if careful technique is not used. Another consideration is whether regional anesthesia should be used when biopsy samples are being collected or a resection is being performed in an area that may contain neoplastic cells. Placement of regional anesthesia in an area containing neoplastic cells could push those cells away from the original tumor margins; therefore, caution should be exercised when performing regional blocks in an area that may be neoplastic.

Anatomic landmarks for the most commonly used regional anesthesia techniques are the infraorbital foramen, mandibular foramen, angular process, and the facial vascular notch (FIGURE 1). Innervation to the maxilla, and hence the nerve(s) that innervate the dental structures and surrounding soft tissues, is supplied by the infraorbital nerve, which is a branch of the maxillary nerve and its associated branches. Innervation to the mandible is supplied by the inferior alveolar branch of the mandibular nerve.

Cranial Infraorbital Nerve Block

The cranial infraorbital nerve block inhibits stimulation to the following nerves: infraorbital, incisivomaxillary, rostral superior alveolar dental, external nasal, internal nasal, and superior labial.14 This block desensitizes the maxillary first, second, and third premolars, canine, and incisor teeth on the same side on which the block is administered. It also desensitizes the associated soft tissues, skin of the muzzle, and the upper lip on the ipsilateral side of block administration.14

To perform the cranial infraorbital block in the dog, palpate the infraorbital foramen as a depression in the alveolar mucosa apical (dorsal) to the distal root of the maxillary third premolar or the mesial root of the maxillary fourth premolar. In the cat, the infraorbital foramen is located at the mesial aspect of the third premolar. The needle should be inserted just into the canal (FIGURE 2), parallel with the canal or directed slightly ventral to it. If you insert the needle apically (dorsally), it could penetrate the retrobulbar space or the globe of the eye. If you insert the needle too far ventrally, it could contact the floor of the infraorbital canal, preventing insertion deeper into the canal. The chosen drug, after appropriate dose calculation, should then be slowly injected into the canal. The drug should be infused into the canal rather than infiltrated directly into the nerve. To prevent intravascular infusion, after inserting the needle into the canal, rotate the syringe 360 degrees, aspirating at each quarter turn. After injection into the canal, remove the syringe and apply digital pressure to the opening of the infraorbital canal for 1 minute.

Caudal Infraorbital (Maxillary) Nerve Block

The caudal infraorbital nerve block inhibits stimulation to the following nerves: maxillary; infraorbital; caudal, middle, and superior alveolar dental; incisivomaxillary; and rostral superior alveolar dental.14 This block desensitizes the maxillary 1st and 2nd molars and all premolars, canine, and incisors of the ipsilateral quadrant.14 Also blocked are the bone and soft tissues of the maxilla on the ipsilateral side of block administration, along with the skin of the nose, cheek, and upper lip on the ipsilateral side.14

The technique for the caudal infraorbital nerve block is identical to that for the cranial infraorbital nerve block. The needle should be inserted into the canal and directed approximately half the length of the zygomatic arch (FIGURE 3). The direction of the needle should be parallel with the canal. If the needle is inserted apically (dorsally) or ventrally, the problems described above can occur. The same injection procedure described for the cranial infraorbital block should be followed, ending with digital pressure to the rostral opening of the canal for 1 minute.

Other approaches to the caudal infraorbital block include the subzygomatic approach and a technique using the maxillary tuberosity. However, because of variations in skull type and breed, we prefer the approach described above.

The technique for the caudal infraorbital nerve block is identical to that for the cranial infraorbital nerve block.

Caudal Inferior Alveolar Nerve Block

FIGURE 4. Appropriate placement of the needle for the intraoral approach to the caudal inferior alveolar (caudal mandibular) nerve block. (A, B) Canine cadaver. Note that the gloved hand is on the external surface of the patient and is palpating the angular process. (C) Feline cadaver.

The caudal inferior alveolar nerve block inhibits innervation to the inferior alveolar branch of the mandibular nerve before it dives into the mandible; to the caudal, middle, and rostral mental nerves; and to the incisive nerve.14 Anesthesia to this region desensitizes all teeth (incisors, canine, premolars, molars), associated labial tissues, the rostral lower lip, and the rostral intermandibular tissues on the side in which it is placed.14 There are 2 approaches to the caudal inferior nerve block: intraoral and extraoral.

FIGURE 5. Intended location of the caudal inferior alveolar (caudal mandibular) nerve block. The block should be administered at the opening of the mandibular foramen. This structure is located half the distance between the location of the alveolar crest distal to the last molar and the angular process. (A) Canine mandible, lingual aspect. (B) Feline mandible.

Intraoral Approach: To perform this block, palpate the angular process of the mandible on the external surface of the patient. This is a palpable prominence located at the caudal-most aspect of the mandibular body (FIGURE 1, A, B, E, F). Insert the needle intraorally through the gingiva at the location of the distal aspect of the mandibular third molar in the dog or the mandibular first molar in the cat (FIGURE 4). Then insert the needle on the lingual aspect of the mandible, as opposed to the buccal surface, directed toward the angular process, attempting to palpate and deposit the block at the opening of the mandibular foramen (FIGURE 5). The opening of the mandibular foramen is located half the distance between the alveolar crest distal to the last molar and the angular process of the mandible. After the needle is inserted into the region of the mandibular foramen, the syringe should be rotated 360 degrees, aspirating at each quarter turn. Because this foramen and nerve may be difficult to palpate, you can place the local anesthetic along periosteum of the body of the mandible in the location of the mandibular foramen, which should cause the local anesthetic to spread over a large surface area. After withdrawing the syringe, apply digital pressure to the area of the foramen for 1 minute to allow the block to diffuse within the tissues.

FIGURE 6. Location of the facial vascular notch on an anesthetized dog. For the caudal mandibular nerve block, the needle is inserted through the skin and directed on the lingual aspect of the mandible for half the width of the mandible in the location of the mandibular foramen.

Extraoral Approach: To perform this block, palpate the facial vascular notch (FIGURE 1, A, C, D). This structure is located on the ventral aspect of the caudal mandible. The needle should be inserted directly through the skin in the middle of this structure (FIGURE 6), directed parallel with the lingual aspect of the mandible and continued dorsally to half the width of the mandible (FIGURE 7). This is the location of the mandibular foramen, similar to the intraoral approach. As described for the intraoral approach because this foramen and nerve may be difficult to palpate, you can place the local anesthetic alongside periosteum of the body of the mandible in the region of the mandibular foramen, which should cause the local anesthetic to spread over a large surface area. Injection technique is the same as above.

DISCUSSION

FIGURE 7. (A, B) Canine skull showing the location of the mandibular foramen identified by using the facial vascular notch.

Multimodal pain-relieving efforts should be pursued for canine and feline patients. Just because our patients cannot communicate their pain to us does not negate the fact that they are experiencing pain. Regional anesthesia, especially when combined with an opioid, can provide a more comfortable procedure for our patients and a more satisfying experience for our clients. When safe technique is used, regional anesthesia not only helps the dentistry and oral surgery patient but also increases client satisfaction. Regional anesthesia reduces the general anesthetic requirement, provides intraoperative and postoperative pain relief, and contributes to a smoother postoperative recovery. These benefits increase client satisfaction by making the patient’s postoperative recovery more comfortable and allowing the patient to be discharged with less drug hangover. Clients expect the same services for their pets as they do for themselves. We can reduce their concerns about use of general anesthesia for dental cleaning patients if at the time of discharge, our patients are awake, pain-free, and able to ambulate as well as when they came in that morning.

Learning Objectives

Upon completion of this article, the reader will be able to describe the processing of pain in the canine and feline patient. After reading the article, the reader will be able to recognize common regional anesthesia techniques commonly used in dentistry and oral surgery procedures.

TOPIC Overview

This article describes regional anesthesia techniques for dentistry and oral surgery procedures in the canine and feline patient. It includes information on medications and dosages that can be used, regional anatomy to be aware of when performing the local blocks and written and photographic diagrams explaining techniques.

The article you have read has been submitted for RACE approval for 1 hour of continuing education credit and will be opened for enrollment when approval has been received. To receive credit, take the approved test online for free at vetfolio.com/journal-ce. Free registration on VetFolio.com is required. Questions and answers online may differ from those below. Tests are valid for 2 years from the date of approval.

Which of the following statements regarding pain is incorrect?
a. Pain is a sensory or emotional experience associated with actual or perceived tissue trauma that is perceived as unpleasant.
b. The purpose of pain is to allow a reaction from the body to prevent additional trauma or damage to an affected area.
c. The incapability to communicate pain negates the possibility that pain is being experienced by the patient.
d. Painful perception can range from an over exaggeration of pain to a painful response from something that is not normally painful.

Which statement best describes the definitionof allodynia?
a. An exaggerated response to a painful stimulus
b. A response to something not normally perceived as painful
c. Associated neurons are repeatedly firing at a lower threshold
d. The insensibility to pain without loss of consciousness

When tissue is injured, the painful response is processed by the central nervous system through:
a. Perception
b. Modulation
c. Transmission
d. Nociception

Which of the following statements regarding regional anesthesia is incorrect?
a. Lidocaine is a regional anesthetic medication with a short onset and a short duration of action (60-120 minutes).
b. Bupivacaine has long duration of action (4-10 hours), and its time of onset is longer than lidocaine.
c. Dogs are significantly more sensitive to the side effects of lidocaine when compared to cats.
d. The maximum dose of bupivacaine that should be administered to a cat as a regional anesthetic agent is 2 mg/kg.

Which of the following statements regarding the addition of buprenorphine to bupivacaine when performing local and regional anesthesia is correct?
a. When buprenorphine is added to bupivacaine, a 3-fold increase in the duration of action of the local anesthetic was seen with patients.
b. The minimum alveolar concentration of isoflurane required for patients was increased when the combination of bupivacaine and buprenorphine was used.
c. Studies have shown that when buprenorphine is added to bupivacaine, the combination block will last less than 4 hours post administration.
d. The recommended amount of buprenorphine to be added to the bupivacaine for a regional anesthetic block is 15 mg/kg.

True/False. When considering placement of a local block in an area that may contain neoplastic cells (biopsy or surgical resection), the administrator should not be concerned about transporting abnormal cells beyond the margins of the original tumor.
a. True
b. False

Which of the following statements concerning local blocks is incorrect?
a. The cranial infraorbital nerve block desensitizes the maxillary 1st, 2nd, and 3rd premolars, canine teeth and incisor teeth on the ipsilateral side of administration.
b. The caudal infraorbital nerve block desensitizes all maxillary premolars, incisors, and canine teeth as well as the maxillary molars on the ipsilateral side.
c. The caudal inferior alveolar nerve block (intraoral) desensitizes the incisors, canine, premolars and molars on the ipsilateral side of administration.
d. The rostral inferior alveolar nerve block (extraoral) desensitizes the incisors, canine, premolars and the 1st and 2nd mandibular molars on the ipsilateral side.

You are presented with a 13-year-old, spayed female West Highland White Terrier that you diagnose with stage 4 periodontal disease. You decide that the right maxillary 4th premolar (108), right maxillary 1st and 2nd molars (109, 110) and the left mandibular canine tooth (304) need to be extracted. Which of the following regional anesthetic blocks should be placed to provide intraoperative and post-operative pain relief?
a. Right caudal inferior alveolar and left caudal infraorbital nerve block
b. Right cranial infraorbital and left rostral inferior alveolar nerve block
c. Right caudal infraorbital and left rostral inferior alveolar nerve block
d. Right caudal infraorbital and left caudal inferior alveolar nerve block

True/False: The intraoral approach to the caudal inferior alveolar nerve block deposits the regional anesthetic medication at the same location as the extraoral approach, which is at the middle mental foramen.
a. True
b. False

Which of the following statements is correct regarding placement of the cranial infraorbital nerve block?
a. The infraorbital foramen in the dog is located at the mesial aspect of the maxillary 1st premolar tooth.
b. The infraorbital foramen in the cat is located at the mesial aspect of the maxillary 2nd premolar tooth
c. The infraorbital foramen in the dog is located at the distal aspect of the maxillary 3rd premolar tooth.
d. The infraorbital foramen in the cat is located at the distal aspect of the maxillary 4th premolar tooth.

NOTE Questions online may differ from those here; answers are available once CE test is taken at vetfolio.com/journal-ce. Tests are valid for 2 years from date of approval.